I have never sexted the wrong person, fortunately. I did send an embarrassing text to the wrong person a couple weeks ago. I meant to send my ex a short text bitching about him not having gotten back to me yet about scheduling plans for thanksgiving for our son (this was 2 days before thanksgiving, so I had a right to bitch). Not sure who I got, but the reply said something along the lines of "Dude, you got the wrong number. Sucks that he's a dick though".
I laughed so hard at the reply and being called "dude" that it made up for my embarrassment.